The invention relates generally to a cutting insert to be placed into a tool holder for boring holes into metals. More specifically, the invention relates to a cutting tool insert having a specialized geometry at the web of the insert, allowing increased stability at various feed rates.
Drilling systems are frequently used to provide cylindrical holes in metallic workpieces. The cutting or boring action of the drill system may be carried out by an elongated, substantially cylindrical drilling tool, such as a combination of a tool holder and a drill insert, which is selectively attached thereto. Such an arrangement may then be used in an application wherein one end of the tool holder is securely mounted in a driving apparatus, which rotates the holder about its longitudinal axis. At the opposite end of the elongated tool holder, the cutting insert engages the material to be cut. Alternatively, the workpiece may be made to rotate relative to the holder and cutting insert, such as in positioning the holder in the tail stock of a lathe or the like. Further, the tool and workpiece may be made to rotate relative to one another. The use of cutting inserts allows for quick changing of the insert upon wear of the cutting surfaces instead of the entire tool, and allows for one tool to be used for a variety of different boring applications by simply changing the insert and not the entire drill assembly.
One problem with prior art cutting tools is that the point or tip of the insert does not efficiently cut into the workpiece. This is due to negative or neutral rake angles formed by web thinning techniques near the chisel of the insert. This results in deformation of the workpiece rather than cutting, which increases the heat produced at the drill insert point. Furthermore, the prior art insert geometry could result in instability, which can cause deviations in the dimensions of the hole being bored, also known as runout and/or bellmouthing which is undesirable. Additionally, prior art drill systems and inserts were configured such that chips from the drilling process were not formed efficiently, causing deterioration of the cutting surfaces. The configuration of the cutting surfaces also did not allow for producing positive rakes in association with chip removal flutes to facilitate chip formation.
The present invention provides a novel drill insert having a V-notched web. The V-notched web allows greater stability and feed rates, while decreasing the heat generated at the insert tip. The stability of the V-notch can further enhance the self-centering capability of existing self-centering configurations of drill inserts. These and other objects of the invention are provided by a drill insert comprising a drill insert body having at least two cutting edges, a web between the two cutting edges, and a web thinning notch formed on either side of the web. Each web thinning notch forms a notch cutting edge having a positive rake angle. These and other objects of the invention are also provided by a drilling tool assembly comprising a holder having a body portion and a head portion, the head portion having a recess formed on one end thereof and a drill insert body securedly insertable within the recess of the holder. The drill insert body has at least two cutting edges, a web between the two cutting edges, and a web thinning notch formed on either side of the web. Each web thinning notch forms a notch cutting edge having a positive rake angle.